CO2 promotes penetration and removal of aqueous hydrocarbon surfactant cleaning solutions and silylation in low-k dielectrics with 3 nm pores

CO2 promotes penetration and removal of aqueous surfactant cleaning solutions in methylsilsesquioxane (MSQ) low dielectric constant (k) films with 3 nm hydrophobic open pores. The films were characterized by mercury probe dielectric constant (k value) measurements and FTIR spectroscopy. Penetration of a solution of 2 wt.% polyoxyethylene 2,6,8-trimethyl-4-nonyl ether, 5b-C12E8, in H2O at ambient pressure increased the k value of etched and N2/H2 ashed JSR 5109 pMSQ from 2.5 to 7.6, indicating 68% of the total pore volume was filled with the solution. This level of penetration was corroborated by the OH peak at 3150–3560 cm−1 and the CH3 peak (surfactant) at 2800–3000 cm−1. Rapid removal of the surfactant solution was achieved by rinsing and drying with 10 mL/min supercritical carbon dioxide (scCO2) at 45 °C and 10 MPa for 2 min. Both water and surfactant are dissolved and emulsified into CO2. Nearly complete removal of the surfactant and water was observed in the k value, which dropped to 2.5, and in the OH and CH3 peak areas. In addition, the cleaning and drying steps may be integrated with silylation in CO2 to remove silanol groups and to add carbon to further reduce the k value. After rinsing and drying with CO2, silylation with 1 wt.% hexamethyldisilazane (HMDS) in CO2 at 45 °C and 10 MPa followed by annealing at 380 °C for 60 min led to a k value of 2.3, near the original value of 2.15. The ability of CO2 to lower the magnitude of the capillary pressure well below the total pressure facilitates removal of the surfactant solution during rinsing and drying. These results suggest that aqueous surfactant solutions, mixed with CO2, may offer significant advantages for cleaning and drying patterned low-k dielectric insulators, particularly as the feature size shrinks below 50 nm and capillary forces become significant.